Hey chovy, I would think the first step would be to determine if they are using bots or human farms.
The company I work for offers solutions to control unwanted automated processes but in particular we have a free product which will help you get a much more concrete idea as to how bad your problem really is. The product is called BotAlert (http://www.pramana.com/botalert/), it installs a lot like Google Analytics and will get you a daily report detailing your human vs non-human activity for the pages you choose to install the code. It is 100% free so please don't think I am trying to get you to buy anything.
I hope that helps!
--David